The invention relates to surgical products, and in particular, to surgical reamers for cutting shaped cavities in bone.
In order to produce a shaped cavity in bone for a hip implant, which requires smooth walls and accurate shape, it is advantageous that the reamer shell or cutting bowl be hemispherical. Further, the cutting teeth must be properly located and oriented.
It is increasingly important, especially with cementless hip surgery, that the acetabulum be reamed to an exact form, generally a hemisphere, thus allowing optimal contact between the bone and the definitive (usually hemispherical) implant.
Further, there is increasing emphasis on cutting a smaller incision to minimize the trauma to the patient and to improve the rate of recovery. Meeting this additional requirement provides an additional challenge to the designers of medical instruments and implants. In addition, the change in surgical procedure includes the fact that the surgeon now more often maintains the acetabular reamer handle on a single axis rather than performing the step of “sweeping” the end of the tool handle through an angle and thus continuously changing the axis of the reamer cut. When a prior art reamer handle is powered, pressed against the acetabulum and maintained on a constant axis such as that described in U.S. Pat. No. 6,001,105, to Salyer, filed Jan. 19, 1998, a series of concentric rings are cut that, on a macro-scale, approximate a hemisphere. When the surgeon “sweeps” the axis of the reamer handle, these irregularities are removed (in a similar manner to polishing) yielding a hemispherical surface. In an attempt to overcome this problem, U.S. Pat. No. 5,116,165 to Sayler, the content of which is incorporated herein by reference, describes a reamer having a limited number of discrete blade-like teeth, which therefore cuts a spline more approximating a perfect hemisphere. Despite the mention of these references as “prior art”, nothing herein should be construed as an admission that the present invention is not entitled to antedate such material by virtue of prior invention.
The inventor(s) of the instant application have also invented a reamer that does not requiring a sweeping operation, such reamer being described in U.S. patent application Ser. No. 10/500,944, entitled “Contour Reamer Teeth”, filed Jan. 16, 2003, the content of which is incorporated herein by reference thereto.
Re-surfacing of the hip has become popular. There is accumulating evidence that minimal Resection of the femoral head is an effective alternative procedure. Surgeons now consider that the same principle should be applied to the acetabulum and the bone should only be minimally resected prior to cup placement (such as described in an article entitled A randomized study comparing resection of the Ace tabular bone at resurfacing and total hip replacement.  P. A. Vendittoli et al. JBJS Br 2006 88-B: 997-1002, the content of which are incorporated herein by reference).
Minimal resection is particularly applicable to the acetabulum as it has a paper-thin translucent floor which can sometimes be damaged when using a conventional hemispherical reamer, given that sweeping using a conventional reamer cannot be avoided, and so the full hemispherical shape of the sweep can sometimes break through this thin floor.
Study of the anatomy of the acetabulum shows that articulation occurs only on the C-shaped articular surface and not on the fovea/acetabular fossa (the floor). In other words, there is no need to cut, resurface or resect the apex area of the acetabulum, and consequently, it should be avoided.
Therefore, what is needed is a reamer that reams on the outer areas of the acetabulum and not the paper-thin translucent floor.